Cotechino with Warm Lentil Salad

Name: Cotechino with Warm Lentil Salad
Ingredients: 1 lemon, zested and juiced; 1 quart chicken stock; 1 rib celery plus 3 tablespoons fine diced celery; 1 small carrot peeled and halved; 1 sprig fresh thyme; 1 teaspoon minced garlic; 1/2 onion; 2 plum tomatoes, seeded and diced fine; 2 tablespoons chopped herbs (parsley, thyme, oregano); 2 tablespoons minced shallots; 3/4 pound cotechino or fresh sweet Italian sausage, sliced in 1/2 lengthwise; 6 tablespoons extra virgin olive oil, divided; 8 ounces Italian, Beluga or French lentils, rinsed under cold water and picked over; Coarsely chopped fresh Italian parsley leaves, for garnish; Salt and freshly ground black pepper